At the end of 2008, DreamWorks Animation bossman Jeffrey Katzenberg embarked on a cross-country tour, toting 20 minutes’ worth of Monsters vs. Aliens. The reason for his trek? To convince critics that 3-D movies are no longer the snake-oil salesman’s hustle, but the future of filmmaking—if not the very savior of big-screen cinema. “Emotionally immersive,” the prophet called it. The Last Word in “the shared communal experience.”

The 5-year-old sitting beside me at a preview screening of Monsters vs. Aliens last weekend offered his own endorsement not 10 seconds into the movie—around the time chunks of blown-up planet appeared to land in his lap. “Whoa, Dad,” he said. “Awesome.” The chorus of children around us agreed, as the theater echoed with giggles, squeals and the random bleats of adolescent amazement.

Carry a big shtick

Directed by Rob Letterman and Conrad Vernon from a screenplay written by more than half a dozen, Monsters vs. Aliens will heretofore be known as the first 3-D movie to genuinely and effectively and astoundingly merge screen and theater, actors (well . . .) and audience—it’s The Purple Rose of Cairo come to life, starring a gelatinous blue blob named Bicarbonate Ostylezene Benzoate . . . or B.O.B. The movie renders all previous comers headache-inducing charlatans, rinky-dink pretenders. For the first time in the medium’s history, you are there—from the president’s war room (shades of Dr. Strangelove) to a prison facility where the government’s been storing assorted mutants and monsters collected since the 1950s.

Of course, such places, plot points and predicaments—and the attempt to shove them and a red paddle ball in your face—have been around just as long; Monsters vs. Aliens is a tomorrow very much indebted to movie’s yesterdays. B.O.B. (voiced by Seth Rogen, nearly as genius a move as the 3-D) has slithered out of Irvin Yeaworth Jr.’s 1958 Z-grade classic The Blob, but this time, the blob’s a former ripe-red tomato injected with ranch-flavored dessert topping, thus rendering him a shape-shifting stoner, a blissfully self-aware naïf with a crush on lime-green Jell-O. Will Arnett voices the Missing Link, a defrosted ape-fish known for terrorizing spring breakers on Cocoa Beach back in 1961; only the Link can communicate with Insectosaurus, a 350-foot-tall silk-snotting grub who has been exposed to nuclear radiation. The film even comes with its very own version of Vincent Price: Hugh Laurie as Dr. Cockroach, the mad scientist who sports the noggin of a cockroach and the bwah-haw-haw of his fiendish ancestors.

Reese Witherspoon is more or less the film’s star: Susan Murphy of Modesto, turned a lovely shade of glowing green by a stray meteorite on the day she was to wed an ambitious weatherman named Derek (Paul Rudd), who’s not terribly well-equipped to deal with a suddenly 50-foot-tall fiancee. The egomaniacal Derek, looking to make the move to bigger-market Fresno, can’t live in a shadow that size. Which is just as well: Susan is woman, hear her roar as Ginormica, rounded up by the government and recruited to save the planet from the invading five-eyed, self-aggrandizing blowhard Gallaxhar (voiced by Rainn Wilson, who has turned being a self-aggrandizing blowhard into an art form).

That’s the story: alien-invasion camp commingled with yet another Dr. Strangelove paranoia parody, strictly playbook material. DreamWorks’ kidult-friendly pop-culture mash-ups—Shrek (as disposable as an episode of Best Week Ever rebroadcast two years later), Bee Movie (nothing more than a way-too-long episode of Seinfeld) and Over the Hedge (admit it, you forgot all about that one)—banked the funds that paid for Monsters’ R&D. They were stepping stones to the mountaintop: the ultimate interactive mash-up, the cinematic equivalent of what Nintendo offered gamers with the Wii, the you-are-there experience.

Monsters vs. Aliens was conceived from the jump as a 3-D work, so every plot point is tethered to the attendant visual bang—the waves of heat emanating from the military’s attack on a mountainous alien probe; the slabs of concrete falling off the Golden Gate Bridge as it disintegrates into the bay; the armies of clones marching through Gallaxhar’s cavernous spaceship; the vast spaces of the Area 51 prison, which looks as though it reaches back a good half-mile.

But children who see the movie on DVD in a few months will wonder what happened to their roller coaster as it morphs into little more than a bumper-car ride. Take away the 3-D, and this is significantly more slight than, say, Madagascar 2 or Kung Fu Panda, DreamWorks movies that had to rely more on the clever factor than the wow factor. The chasm between Monsters vs. Aliens’ technical accomplishment and artistic achievement is vast: The story’s familiar, and as good as the performers are, they’re still doing their trademark shtick (though Stephen Colbert as the president is a stroke of casting brilliance). But the grandeur of the effects—the honest-to-God spectacle of the thing—elevates Monsters vs. Aliens to something approaching art. It’s not a masterpiece, but it’s most certainly a milestone.